German Published Patent Application No. 10 2008 044 858 describes an optical position-measuring device that is suitable for detecting the position of two objects movable relative to each other in at least one measuring direction. To that end, the position-measuring device includes a measuring standard which is joined to one of the two objects. The measuring standard has an incremental graduation extending in the measuring direction, as well as at least one reference marking at a reference position. The reference marking provides a reference point for the high-resolution, incremental position measurement, to which the incremental measurement is related after the reference marking has been crossed and a reference signal has been generated. Moreover, the position-measuring device includes a scanning unit which is joined to the other of the two objects and which has a divergently emitting light source, one or more gratings, as well as a reference-signal detector system. German Published Patent Application No. 10 2008 044 858 describes in detail how, in an optical position-measuring device based on a scanning principle using divergent lighting, what are termed chirped reference markings are able to be utilized to generate a high-resolution reference signal.
In this position-measuring device, the reference marking is located in a separate reference track adjacent to an incremental track having the incremental graduation on the measuring standard. For this reason, the position of the reference signal relative to the incremental signals is a function of the angle of twist between the measuring standard and the scanning unit about an axis which is oriented perpendicularly to the plane of the measuring standard. In this context, the smaller the graduation period of the incremental graduation and the greater the distance of the scanning centroids for the incremental track and reference-mark track perpendicular to the measuring direction, the greater the sensitivity with respect to such a twisting. However, the defined position and width of the generated reference signal relative to the incremental signals are of great importance for the correct further processing of the reference signal.
The position of the reference signal is usually set by a troublesome mechanical adjustment of the scanning unit. The width of the reference signal may be effected by the selective change of comparator trigger thresholds which the respective analog current pulse or voltage pulse must exceed or drop below during the signal processing in order to generate the rising edge or the cut-off edge of the reference signal. However, especially when working with high-resolution optical position-measuring devices, the expenditure for such a mechanical and electrical adjustment is considerable.